MARINE MAMMAL SCIENCE, 29(4): E448–E462 (October 2013)© 2013 Society for Marine MammalogyDOI: 10.1111/mms.12044

Spatial and temporal analysis of killer whale (Orcinus orca)strandings in the North Pacific Ocean and the benefits of a

coordinated stranding response protocol

MICHELLE M. BARBIERI,1, 2 UC Davis Wildlife Health Center–Orcas Island Office, 942 DeerHarbor Road, Eastsound, Washington 98245, U.S.A.; STEPHEN RAVERTY, British Columbia

Ministry of Agriculture and Food, Animal Health Center, 1767 Angus Campbell Road,

Abbotsford, British Columbia V3G 2M3, Canada and University of British Columbia, 2202

Main Mall, Vancouver, British Columbia V6T 1Z4, Canada; M. BRADLEY HANSON,NOAA/NMFS/Northwest Fisheries Science Center, 2725 Montlake Boulevard, East Seattle,

Washington 98112, U.S.A.; STEPHANIE VENN-WATSON, Epitracker Analytics, 2165

Historic Decatur Road, San Diego, California 92106, U.S.A.; JOHN K. B. FORD, PacificBiological Station, Fisheries and Oceans Canada, 3190 Hammond Bay Road, Nanaimo,

British Columbia V9T 6N7, Canada; JOSEPH K. GAYDOS, UC Davis Wildlife Health

Center–Orcas Island Office, 942 Deer Harbor Road, Eastsound, Washington 98245, U.S.A.

Abstract

Killer whales (Orcinus orca) are widely distributed throughout the world’s oceans,yet little has been documented about their stranding patterns. Knowledge of strand-ing patterns improves our ability to examine and sample carcasses and provides afoundation for understanding killer whale natural history, diet, reproduction,anthropogenic stressors, emerging diseases, and patterns of unusual mortality. Wecompiled published and unpublished killer whale stranding data to describe strand-ing patterns in the North Pacific Ocean. Between 1925 and 2011, 371 strandedkiller whales were reported in Japan (20.4%), Russia (3.5%), Alaska (32.0%), Brit-ish Columbia (27.4%), Washington (4.0%), Oregon (2.7%), California (5.1%),Mexico (3.8%), and Hawaii (0.8%). Strandings occurred at all times of year, butregionally specific seasonal differences were observed. Mortality and annual censusdata from Northern and Southern Resident populations were extrapolated toestimate that across the North Pacific, an average of 48 killer whales die annually.However, over the last two decades, an average of only 10 killer whale carcasses wererecovered annually in this ocean, making each event a rare opportunity for study.Publication of a standardized killer whale necropsy protocol and dedicated fundingfacilitated the number of complete postmortem necropsies performed on strandedkiller whales from 1.6% to 32.2% annually.

Key words: killer whales, Orcinus orca, stranding, North Pacific Ocean, disease,necropsy.

1Corresponding author (e-mail: barbierim@TMMC.org).2Current address: The Marine Mammal Center, 2000 Bunker Road, Sausalito, California 94965, U.S.A.

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Killer whales (Orcinus orca) are cosmopolitan cetaceans (Dahlheim and Heyning1999). Despite their worldwide distribution and the history of intense study of somepopulations, few analyses of killer whale stranding patterns have been conducted.Historically, strandings have been an important method for studying marine

mammals. They have demonstrated the existence of new marine mammal species,provided details on prey preference, growth rates, age at maturity, gestation, repro-ductive seasonality, longevity, and have expanded our understanding of marine mam-mal mortality factors including infectious diseases and toxins (Geraci and Lounsbury2005, Morin et al. 2010). More recently, information gained from stranded marinemammals has enhanced our understanding of the impacts of sonar and underwaterdetonations (Jepson et al. 2003, Fernandez et al. 2005, Danil and St. Leger 2011)and further characterized injuries caused by vessel-whale collisions (Campbell-Maloneet al. 2008). Stranding data have proven to be an early warning system for identifyingthe impacts of fishing bycatch in species like bottlenose dolphins (Tursiops truncatus;Byrd et al. 2008). Also, over sufficiently long time intervals, stranding records haveeven been shown to yield a richer assemblage of species than line transect surveymethods (Pyenson 2010) and could be capable of detecting population declinessooner than survey data (Gulland 2006). Advances in both technology (e.g., polymer-ase chain reaction [PCR]) and expertise have helped identify novel and emergentpathogens in stranded specimens and evaluate their potential impact on reproductionand population health (e.g., Gibson et al. 2011, Nymo et al. 2011). Marine mammalstranding patterns can also reflect exposure to stressors such as biotoxins, contami-nants, and climate change and help elucidate the synergistic effects of environmentalperturbations and emerging pathogens (Krahn et al. 2004, Flewelling et al. 2005,Fire et al. 2007, Moore 2008, Van Bressem et al. 2009, Bossart 2011). As long-livedtop predators, marine mammals are sentinel species for recognizing the cumulativeimpacts of such stressors and facilitate our overall understanding of aquatic ecosystemhealth (Jessup et al. 2004, Wells et al. 2004, Evans et al. 2005, Moore 2008, Bossart2011). Thus, strandings offer opportunities to collect data on marine mammalbiology and health, which are particularly central to conservation and managementdecisions for declining populations.The U.S. National Marine Fisheries Service (2008) mandated improved killer

whale stranding response as part of a comprehensive effort to better define causes ofkiller whale mortality and inform conservation efforts in the case of the Southern Res-ident killer whale distinct population segment (DPS) in the eastern North Pacific.This killer whale DPS is listed as endangered in the United States (U.S. FederalRegister 2005) and Canada (Baird 2001, Committee on the Status of EndangeredWildlife in Canada 2008). Concomitant with this designation, a comprehensive killerwhale necropsy and disease testing protocol (Raverty and Gaydos 2004), designed toimprove killer whale stranding response, was released. One objective of the presentstudy was to compare the level of killer whale stranding response before and after thepublication and circulation of this protocol to evaluate the effectiveness of this tool.Threats to killer whales can be better understood through comprehensive strand-

ing investigations, particularly when combined with long-term population monitor-ing studies, such as those conducted for resident killer whales in the North Pacific.These threats include prey limitation, environmental contaminants, disease, vesseldisturbance, and a small population size (Gaydos et al. 2004, Wiles 2004, U.S.National Marine Fisheries Service 2008, Ford et al. 2010). Gross and microscopicexaminations of stranded carcasses are the cornerstone of comprehensive strandinginvestigations, but should be interpreted in the context of spatial and temporal

BARBIERI ET AL.: KILLERWHALE STRANDINGS E449

patterns in mortalities. Norman et al. (2004) examined the seasonality of 16 killerwhale strandings in Washington and Oregon; however, despite the potential value,no comprehensive ocean-wide analysis of killer whale strandings has been published.The present study used published and unpublished data to summarize and illustratethe spatial and temporal aspects of killer whale strandings in the North Pacific Oceansince 1925.Increased stranding preparedness will improve data collection on diseases, contam-

inants, and causes of mortality for this endangered population and for killer whalesworldwide. In the case of Southern Resident killer whales (SRKW), contaminantburden is thought to contribute to their decline (Wiles 2004, U.S. National MarineFisheries Service 2008). In fact, SRKW and sympatric killer whales of the marinemammal eating ecotype (Ford et al. 1998) have been found to harbor some of thehighest levels polychlorinated biphenyls (PCBs) among all cetaceans (Ross et al.2000). Although results from chemical analyses of biopsied blubber samples canprovide valuable information when carefully interpreted (Ross et al. 2000, Krahnet al. 2004), internal organ and multiple, full-thickness blubber samples can beobtained from stranded animals (Yordy et al. 2010). This allows a more thoroughassessment of whole body contaminant burden and associated potential healthimpacts.In the mid-1990s, the Northern and Southern Resident killer whale populations

(NRKW and SRKW, respectively) experienced 7% and 18% declines, respectively,which correlated with a coast-wide decline in Chinook (Oncorhynchus tshawytscha)salmon stock abundance indices (Ward et al. 2009, Ford et al. 2010). Observations ofmalnourished animals, however, were rare, suggesting that mortality might not havebeen a direct result of malnourishment. In the face of reduced prey availability, themobilization of lipid stores to provide energy also mobilizes contaminants that havethe potential to reduce immune function and increase disease susceptibility (Rosset al. 2000; Krahn et al. 2007, 2009).Disease is a major mortality factor for many marine mammal species and has been

the cause of numerous mortality events worldwide. Gulland and Hall (2007) reportedan increasing global trend in the reporting of marine mammal infectious diseases andin the documenting of mass mortalities, which are likely associated with an increasein scientific research and in the number of researchers in this field. Despite this, littleis known about diseases of free-ranging killer whales (Gaydos et al. 2004). Deviationsin killer whale strandings from baseline levels suggest unusual mortality events, butare impossible to evaluate without knowledge of common temporal and spatialstranding patterns by region (Gulland 2006).

Materials and Methods

Peer-reviewed and gray literatures were searched for data on killer whale strandingsthroughout the North Pacific Ocean. Records were sought as far back as possible.Direct correspondence with major marine science centers, government agencies, andkiller whale biologists was also undertaken to solicit unpublished killer whale strand-ing and necropsy information. Specifically, we requested the following: strandingdate and location, the number of animals involved, individual animal identification,ecotype, pod, age or age class, total length, sex, whether or not a gross necropsy wasperformed, a list of ancillary tests that were performed, whether or not a diagnosiswas made, and the name of the lead biologist and/or pathologist.

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Using the information gathered, we rated the level of postmortem examinationperformed on a stranded carcass. Where no information was provided, or little ornothing was done to determine cause of death, the necropsy was classified as “no rat-ing.” If a gross necropsy was conducted and biological specimens were collected, theresponse was rated as “intermediate.” For carcasses receiving gross examination,microscopic examination of tissues, as well as bacteriology, toxicology, and otherancillary tests, the necropsy was rated as “complete.” Animals that stranded alive andsurvived were not included in this portion of the analysis.Locations were categorized into the following nine regions of the North Pacific

Ocean: Japan, Russia, Alaska, British Columbia, Washington, Oregon, California,Mexico, and Hawaii. While it is preferable to use total length to classify animals intoage classes, these data were not consistently available so for the purposes of this study,animals were broadly categorized as either “adult” or “subadult.” If an animal wasqualitatively described as immature, neonate, calf, juvenile, or subadult, it was cate-gorized as “subadult.” In rare cases, no descriptive terminology was given, but a totallength was provided. For these animals, females >490 cm and males >550 cm werelabeled as “adult” (Mitchell 1975 as cited in Nowak 1999). Dates were categorizedby month, year, and season north of the equator (Winter: January–March, Spring:April–June, Summer: July–September, and Fall: October–December). The data alsowere queried to describe the occurrence of mass strandings, which are defined as thoseinvolving at least two animals of the same species, excluding cow-calf pairs (Geraciand Lounsbury 2005).Descriptive and univariate analyses were performed. For univariate analyses, cate-

gorical variable comparisons were conducted using chi-square tests with appropriatecontingency tables; categorical and numerical variable comparisons were conductedusing general logistic or general linear models. To compare the likelihood of strand-ing events by region and season, a general linear model was used with post hoc inter-group comparisons using the Scheffe’s method. Statistical significance was defined asP � 0.05.Killer whale stranding density was calculated for each of the nine North Pacific

regions. To compare trends in stranding density across regions, values were standard-ized by 500 km units. The denominator of 500 km was chosen because it is a roundnumber less than the maximum coastline length of the smallest region (Oregon).Each individual mortality in a mass stranding was counted separately for this anal-

ysis, and carcasses that were observed floating offshore were excluded. Shorelinelengths for each of the whale strandings regions were calculated, using ESRI ArcMap10 software, from polygon shapefiles that are included in the ESRI “Maps & Data”collection, 2009 version. The two shapefiles used were “as_cntry.shp” and “na_cntry.shp.” The shoreline for each region was extracted from the polygon shapefileand converted to a polyline shapefile. Line segment lengths were then calculatedusing the “Calculate Geometry” function. The segment lengths were then summedusing the “Statistics” function. The Russia region includes all of the shoreline northof the Russia–China border and terminates at the 180º meridian. The Mexico regionincludes the Baja Peninsula and mainland Mexico to 70 km south of Puerto Vallarta.

Results

Data on 371 killer whales that stranded in 234 events in the North Pacific between1925 and 2011 were obtained (Table 1, Table S1, Fig. 1). Data on sex, age, and

BARBIERI ET AL.: KILLERWHALE STRANDINGS E451

length were provided for a subset of the stranded animals (Table 1). Strandings weredescribed by region as follows: Japan (20.4%), Russia (3.5%), Alaska (32.0%),British Columbia (27.4%), Washington (4.0%), Oregon (2.7%), California (5.1%),

Table 1. Demographic data on stranded killer whales in the North Pacific, 1925–2011.

Demographic Number (% of reported) Total reported

Sex 195Female 96 (49.0)Male 99 (50.7)

Age category 228Subadult 100 (43.7)Adult 128 (56.1)

Median length 554 cm (range 120–1,000) 153Region 371

Japan 76 (20.4)Russia 13 (3.5)Alaska 119 (32.0)British Columbia 102 (27.4)Washington 15 (4.0)Oregon 10 (2.7)California 19 (5.1)Mexico 14 (3.8)Hawaii 3 (0.8)

Figure 1. Killer whale strandings in the North Pacific, 1925–2011. Cities with humanpopulations greater than one million people are noted.

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Mexico (3.8%), and Hawaii (0.8%). The highest density of killer whale strandingsoccurred in Oregon (5.3 whales/500 km shoreline), followed by California, BritishColumbia, and Washington (Fig. 1, Table 2). Data over the past two decades (1990–2010) suggest that on average, 10 killer whale strandings are reported each year inthe North Pacific. No significant sex bias in strandings was noted in the 195 carcassesfor which this information was reported (P = 0.77).Data on total length and/or age class were available for 228 stranded animals.

Overall, the number of adult killer whale strandings (56.1%) exceeded that of subad-ults (43.7%; P = 0.05). This finding is likely driven by the similar pattern found spe-cifically in Alaska, as no significant differences were observed between age classesacross any other region. Of the 67 Alaskan stranding records for which age class wasprovided, 65.7% were adults and 34.3% were subadults (P < 0.01).Annual stranding data suggest that the number of reported killer whale strandings

has increased over time (Fig. 1), however this is likely confounded by increased sur-veillance effort. Throughout the North Pacific Ocean, the greatest number of stran-dings occurred in May (P < 0.01; Fig. 2). When analyzed by region, significantseasonal differences were observed in Alaska, California, Japan, and Mexico. (Table 3,Fig. 3). Stranding events were more likely to occur or be reported in fall and summerin Alaska (P < 0.0001), fall in California (P = 0.0006), winter in Japan (P < 0.0001),and summer in Mexico (P = 0.02). As a whole, the model suggested at least onesignificant seasonal difference among strandings in British Columbia (P = 0.05).However, specific post hoc comparisons of strandings by season did not identify anysignificant differences in this region. No significant differences were observed in theseasonality of strandings in Russia (P = 0.27), Washington (P = 0.81), Oregon (P =0.63), or Hawaii (P = 0.66), although samples were limited in some of these regions.As a whole, the general linear model indicated significant differences among theregions compared (P = 0.05), but no significant post hoc intergroup comparisons wereidentified using Scheffe’s method.Twenty-three (9.8%) of the 234 reported stranding events were mass strandings.

Mass stranding events were reported in five regions (Japan, Alaska, British Columbia,Washington, Mexico) but the majority occurred in Alaska (n = 10 events) and Japan(n = 6 events). Of the 160 individuals that mass stranded, at least 122 mortalities(76.3%) occurred. On average, there were approximately six mortalities per massstranding (range 2–21 animals).

Table 2. Killer whale stranding density (strandings per 500 km of shoreline) in nine NorthPacific regions. Carcasses observed floating offshore were excluded from analysis.

Region Number of strandingsCoastline

length (km) Strandings per 500 km

Japan 76 18,240 2.08Russia 13 37,200 0.17Alaska 110 61,180 0.90British Columbia 98 19,250 2.55Washington 15 3,320 2.26Oregon 10 940 5.32California 19 2,970 3.20Mexico 14 9,200 0.76Hawaii 3 1,944 0.77

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Of the 371 stranded killer whales reported, 328 mortalities were documented. Thepostmortem examinations of 24 of these individuals were rated as complete and 46were rated as intermediate. Examinations of the remaining 258 carcasses were given“no rating.” Since the 2004 publication of a coordinated killer whale strandingresponse and necropsy protocol and increased efforts and funding by NOAA Fisheriesto respond to killer whale strandings, stranding response rates increased significantly(P = 0.02) and a significantly higher number (P < 0.0001) of complete necropsieshave been performed. Prior to publication of the necropsy protocol, an average of only1.6% of carcasses received complete postmortem examinations each year. Since thebeginning of 2004, this value has increased to an average of 32.2% per year.

Table 3. Comparisons of stranding event likelihood by region and season.

Region P Significant intergroup comparisons

Alaska <0.0001 fall, summer > spring, winterBritish Columbia 0.05 noneCalifornia 0.006 fall > summer, winterHawaii 0.66 n/aJapan <0.0001 winter > spring, fall, summerMexico 0.02 summer > winterOregon 0.63 n/aRussia 0.27 n/aWashington 0.81 n/a

Num

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ller w

hale

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Figure 2. Annual reported killer whale strandings in the North Pacific, 1925–2011.

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Discussion

This is the first comprehensive description of the spatial and temporal attributes ofhistorical killer whale stranding patterns in the North Pacific Ocean. While on aver-age, only 10 stranded killer whales are observed annually in this region, it is likelythat more killer whales die than are found or reported. The actual percentage of killerwhales that die compared to those that are beach-cast and observed is unknown, butcan be estimated using data from the well studied SRKW and NRKW populationsfound off the west coasts of the United States and Canada (Ford et al. 2000).Using distinct physical markings and photographic identification, the Center for

Whale Research (Friday Harbor, WA) has conducted an annual census of the SRKWpopulation since 1976. Fisheries and Oceans Canada (Nanaimo, British Columbia,Canada), with help from the Vancouver Aquarium (Vancouver, British Columbia,Canada), has conducted an annual census of NRKW since 1973. According to one ofthe authors (JKBF), 96 SRKW and 176 NRKW are known to have died between1974 and 2008. In that same time period, 19 confirmed SRKW and 5 confirmedNRKW carcasses were found, suggesting carcass recovery rates of 20% and 3% forthe SRKW and NRKW populations, respectively. Using our estimated annual obser-vation rate of 10 strandings/yr in the North Pacific Ocean, and the best-case scenarioof a 20% carcass recovery rate (observed in the SRKW), we can extrapolate thatthroughout the entire North Pacific Ocean, at least 48 killer whales strand annually.This small number of animals further supports the need that every killer whalestranding should be investigated and represents a critical opportunity to learn moreabout the diseases and biology of killer whales in the North Pacific.Mortality data gathered from the annual censuses of resident killer whales

described above were compared to the recovery of resident killer whale carcasses from1974 to 2008 (Fig. 4). As expected, annual census data documented more residentkiller whale mortalities than stranding data alone, on average, by 4:1. An increase inresident killer whale mortality over time is evident in both the annual census and car-cass recovery data. The 20% carcass recovery rate calculated for SRKW is the highestreported for any cetacean species to date (Williams et al. 2011). Despite this rela-tively high rate of carcass recovery, stranding data alone would have been insufficientto document the magnitude of this population decline. Although stranding investi-gations are key to documenting trends in and causes of mortality, they cannot replacelong-term population assessments and demographic data acquired through long-termphoto-identification studies. Rather, these two complementary methods of assessmentshould be used to best identify trends in killer whale population health and threats totheir recovery.Cumulative killer whale stranding density (strandings per 500 km of shoreline)

was greatest in Oregon, California, British Columbia, and Washington. Insufficientdata are available to infer that this represents a greater relative abundance of killerwhales off the northwestern coast of North America, though killer whales are presentyear-round in Washington and British Columbia waters (Ford et al. 2000, Baird2001, U.S. National Marine Fisheries Service 2008). The killer whale populations inthese regions are also studied intensively and comparable survey effort has not beendescribed in other North Pacific sites, such as Japan and Russia. Thus, the higherstranding density observed between California and British Columbia could be biasedby a greater scientific focus on killer whales in these areas. Human population densityand coastline accessibility, relative to killer whale abundance, also could explain therelatively higher stranding density in these regions. From 1930 to 2002, cetacean

BARBIERI ET AL.: KILLERWHALE STRANDINGS E455

strandings in the northwest United States were most often reported in areas regularlyvisited by humans (Norman et al. 2004).Shorelines in the northern portions of the study area are highly convoluted, but the

additional shoreline length does not necessarily represent a larger habitat across whichstrandings can occur. It is therefore possible that stranding density along the northernNorth Pacific states is underestimated compared to regions with relatively straightershorelines.When examined on a monthly basis, killer whale strandings reported in the North

Pacific are most common in May (Fig. 5). Areas in which discrete seasonal differenceswere observed include Alaska, California, Mexico, and Japan (Table 3, Fig. 3). Stran-dings peak in the summer and fall months in Alaska, which could reflect increasedcarcass surveillance in warmer months. No distinct pattern was observed acrossregions, but seasonality of stranding events may be used to guide stranding responseefforts and resource allocation in these areas. Increased collection of stranding data inother regions would better help define trends and direct preparedness efforts in moredisparate locations.Overall, the majority of reported strandings (32%) and mass stranding events

occurred in Alaska. Interestingly, a significant difference between age classes also wasobserved in this region, with a predominance of adult killer whales (P < 0.01). Thir-teen of the 22 adult individuals that were involved in mass strandings in Alaska wereeither pushed back or were able to refloat themselves and swim away. When this sub-set of animals is excluded, there is no significant difference between age classesstranding in Alaska (P = 0.7). Accounts of suspected killer whale predation on belugawhales have been associated with live killer whale mass strandings in Cook Inlet,Alaska (Shelden et al. 2003). Thus, feeding strategies of adult killer whales couldexplain the predominance of adult strandings in this region.

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)dednartslatotfo%(

slaminaforeb

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KAURPJ

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Figure 3. Regional killer whale strandings by season for each of the nine North Pacificregions, 1925–2011. For each region, the number of strandings per season is illustrated as apercent of the total strandings in that region. Seasons are defined as: winter (January–March),spring (April–June), summer (July–September), and fall (October–December). Regions aredefined as: Japan (JP), Russia (RU), Alaska (AK), British Columbia (BC), Washington (WA),Oregon (OR), California (CA), Mexico (MX), Hawaii (HI).

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Comprehensive stranding response enables the collection of data on marine mam-mal life history, genetics, and disease, in addition to causes of mortality. Collectively,the diversity of information gathered from stranded animals is essential in guidingpopulation management and conservation measures. For example, vessel strikes are a

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Annual census mortalities Recovered carcasses

Figure 4. Comparison of carcass recovery data to mortality data obtained by annual censusesof Southern Resident and Northern Resident killer whales, 1974–2008.

Figure 5. Killer whale stranding events in the North Pacific by month, 1925–2011.

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leading cause of mortality in critically endangered North Atlantic right whales(Eubalaena glacialis) (Knowlton and Kraus 2001). Intensive stranding response effortsand postmortem data collection provided the explicit information used in the devel-opment of vessel speed restrictions to reduce the incidence of ship strikes to protectthis endangered species (Moore et al. 2004, U.S. Federal Register 2008). The openaccess online stranding response and necropsy protocol developed for North Atlanticright whales (McLellan et al. 2004) likely facilitated these efforts.Samples from stranded marine mammals also help determine genetic differences,

which can inform stock structure and social organization (Hoelzel et al. 1998, Viricelet al. 2008, Morin et al. 2010, Foote et al. 2011). Samples from stranded killerwhales that are used to evaluate genetic variation will have important managementimplications if the scientific community determines that Orcinus orca should be splitinto multiple species (Morin et al. 2010, Foote et al. 2011). Additionally, strandingdata permit more complete assessments of environmental contaminant exposure(Krahn et al. 2004), and have been used to identify emerging killer whale pathogensincluding Edwardsiella tarda (Ford et al. 2000) and Salmonella Newport (Colegroveet al. 2010).Investigation into the stranding of 12 killer whales entrapped in ice near Aido-

mari, Rause, Hokkaido, Japan, is one example of how multidisciplinary strandingresponse can document natural catastrophic environmental events and maximizeopportunities for sample collection and study. Carcasses were screened for exposure toinfectious diseases, heavy metals, and persistent organic pollutants and described byage and reproductive maturity (Uni et al. 2005, Endo et al. 2006, Kajiwara et al.2006, Omata et al. 2006, Endo et al. 2007, Harino et al. 2008, Haraguchi et al.2009, Amano et al. 2011).Since 2004 there has been a 32% increase in the number of complete necropsies

done on killer whales. The development of a killer whale necropsy and strandingresponse protocol (Raverty and Gaydos 2004), combined with U.S. federal interestand financial resources facilitated this improved response to killer whale strandings.The protocol is available electronically (Raverty and Gaydos 2004), and the develop-ment of similar protocols could improve data collection from other under-studiedmarine mammals. Stranding investigations are an integral component of a compre-hensive population health assessment program, as they yield data on mortality trends,life history, and threats to conservation, such as contaminant exposure and infectiousdisease.The historical data obtained in this study were used to describe monthly and sea-

sonal trends in North Pacific killer whale strandings to guide stranding responseefforts and resource allocation. While these data are likely incomplete, they representthe best current information on killer whale strandings in the North Pacific and illus-trate the importance of continued time and resource allocation to investigate threatsto free-ranging killer whales.

Acknowledgments

We thank the numerous individuals from around the world that provided informationabout killer whale strandings from their region, especially, D. Bain, R. Baird, L. Barrett-Leon-ard, G. Ellis, K. Jackson, C. Kemper, E. Kompanje, A. Mironova, M. Ogino, R. Osborne,E. Poncelet, M. Sternfeld, and K. Wilkinson. The project also would not have been possiblewithout the help of M. Artois, D. Bain, A. Baretto, J. Barnett, K. Barthelmess, M. Berman,

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T. Besser, C. Callahan, P. Calle, L. Dalla-Rosa, P-Y. Daoust, N. Davison, S. DeGuise,H. Dietz, P. Duff, P. Duignan, S. Ferguson, T. Flaherty, M. Fleetwood, K. Flynn, P. Folkens,R. French, C. Fung, S. Gomez de Farias Jr., F. Gulland, P. Hamilton, K. Heise, D. Janiger,A. Jensen, P. Jepson, R. Lewis, D. Look, S. Kennedy, P. Komnenou, T. Kuiken, S. Lair,J. Lein, L. Measures, R. Moeller, T. Morner, M. Morrice, S. Murphy, O. Nielsen, L. Paul,K. Prager, A. Romero, K. Rose, P. Ross, T. Rowles, D. Schofield, A. Shestopalov, E. Stredu-linsky, C. Smeenk, P. Tygrve, M. Uhart, M. VanBressem, O. Van Canneyt, I. Vilchis, E.Wamba, H. Whitney, R. Woods, W. Yang, and T. Zabka who provided contact informationfor killer whale biologists or killer whale stranding information. We thank K. Balcomb, G.Ellis, A. Friedlaender, W. McLellan, and J. Watson for reviewing early versions of this manu-script and for providing constructive comments. This work was supported by a grant fromNOAA Fisheries, as well as by in-kind support from the U.S. Navy and the SeaDoc Society, amarine ecosystem health program of the Wildlife Health Center at the UC Davis School ofVeterinary Medicine (http://www.seadocsociety.org).

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Received: 3 March 2012Accepted: 4 January 2013

Supporting Information

The following supporting information is available for this article online at http://onlinelibrary.wiley.com/doi/10.1111/mms.12044/suppinfo.Table S1. Killer whale strandings in the North Pacific, 1925–2011.

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